Wrought Iron
Introduction
• Wrought iron is a mechanical mixture of very pure iron and a silicate
slag.
• Wrought iron is a ferrous material, aggregated from a solidifying
mass of pasty particles of highly refined metallic iron with which a
minutely and uniformly distributed quantity of slag is incorporated
without subsequent fusion.
Chemical composition
• C – 0.02% - 0.03%
• P – 0.05% - 0.25%
• Si – 0.02% - 0.10%
• S – 0.008-0.02%
• Mn – Nil-0.02%
• Slag – 0.05%-1.50%
• Iron - Balance
Properties
• W.I is never cast.
• Shaping is accomplished by hammering pressing and forging.
• High ductility
• Can be forged and Welded.
• Ultimate tensile strength of W.I. can be increased considerably by cold
working followed by a period of aging.
•
W.I. possesses a high resistance towards the corrosion.
• W.I. possesses the property of recovering rapidly from overstrain, which
enables it to accommodate sudden and excessive shocks without
permanent injury.
• High resistance towards fatigue.
Property
Value
Ultimate tensile strength [psi
(MPa)]
34,000–54,000 (234–372)
Ultimate compression strength
[psi (MPa)]
34,000–54,000 (234–372)
Ultimate shear strength [psi
(MPa)]
28,000-45,000 (193-210)
Yeild point [psi (MPa)]
23,000–32,000 (159–221)
Elongation, % in 200 mm
18-25
Modulus of elasticity (in tension)
[psi (MPa)]
28,000,000 (193,100)
Melting point [°F (°C)]
2,800 (1,540)
Uses and Application
• Building Construction: Underground services lines and electrical
conduit. Soil, waste, vent and downspout piping.
• Public Works: Bridge railings, blast plates, drainage lines, and
troughs, sewer outfall lines, weir plates, sludge tanks and lines.
• Industrial: Condenser tubes, unfired heat exchanges, acid and
alkali process lines, skimmer bars.
• Rail road and marine: Diesel exhaust and air brake piping, ballast
and brine protection plates, hull and deck planting, tanker heating
coils etc.
• Others : Gas collection hoods, coal handling equipment, cooling
tower and spray pond piping.
Cast Iron
ORE
Blast Furnace
PIG IRON
CUPOLA FURNACE
CAST IRON
White CI
Grey CI
Malleabilize
CAST IRONS
Ductile CI
Good castability  C > 2.4%
Malleable CI
Alloy CI
Stress concentration
at flake tips avoided
Gray Cast Iron
• Gray cast iron is characterized by its graphitic microstructure, which
causes fractures of the material to have a gray appearance.
• It is the most commonly used cast iron and the most widely use cast
material base on weight.
• Most cast irons have a chemical composition of 2.5 to 4.0% carbon,
1 to 3% silicon, and the remainder is iron.
• Gray cast iron has less tensile strength and shock resistance than
steel.
• Its compressive strength is comparable to low and medium carbon
steel.
Gray Cast Iron
• A low cost material that can be used for many purposes
Characteristics:
1)
Gray Iron basically is an alloy of carbon and silicon with iron.
2)
It is readily cast into a desired shape in a sand mould.
3)
It contains 2.5-3.8% C, 1.1-2.8%Si, 0.4-1%Mn, 0.15% P and 0.10% S.
4)
It is marked by the presence of flakes of graphite in a matrix of ferrite,
pearlite and austenite.
5)
Graphite flakes occupy about 10% of the metal volume
6)
Length of flakes may vary from 0.05 mm to 0.1 mm
7)
When fractured, a bar of Gray Cast Iron gives gray appearance
8)
Gray iron possesses lowest melting point of the ferrous alloys.
9)
G.C.I. possesses high fluidity and hence it can be cast into complex
shapes and thin sections.
10) It possesses machinability better than steel.
11) It has higher resistance to wear
12) It possesses high vibration damping capacity
13) Gray iron has low ductility and low impact strength as compared
with steel.
14) G.C.I. has a solidification range of 2400 – 2000°F
15) It associates low cost combined with hardness and rigidity.
16) G.C.I. possesses high compressive strength
17) G.C.I. possesses excellent casting qualities for producing simple and
complex shapes.
Application
1)
Machine tools and structures (bed, frame and details)
2)
Gas or water pipes for underground purpose
3)
Manhole covers
4)
Cylinder blocks and heads for I.C. engines
5)
Tunnel segments
6)
Frames for electric motors
7)
Ingot moulds
8)
Sanitary Wares
9)
Piston Rings
Malleable Cast Iron
Malleable iron: dark graphite rosettes (temper carbon)
in an –ferrite matrix
Malleable Cast Iron
• Malleable iron starts as a white iron casting, that is then heat treated at
about 900 °C (1,650 °F).
• Graphite separates out much more slowly in this case, so that surface
tension has time to form it into spheroidal particles rather than flakes.
• In general, the properties of malleable cast iron are more like mild steel
Characteristics:
1)
M.C.I. is one which can be hammered and rolled to obtain different
shapes.
2)
M.C.I. is obtained from the hard and brittle white iron through a
controlled heat conversion process.
3)
(i) A ferritic M.C.I. has Ferrite matrix
(ii) A pearlitic M.C.I. has pearlite matrix
(iii) An alloy M.C.I. contains chromium and nickel and possess high
strength and corrosion resistance.
4)
M.C.I. possess high yield strength.
5)
High young’s modulus and low coefficient of Thermal expansion.
Malleable Iron
Pearlitic Matrix
Ferrite (White)
Graphite (black)
Pearlite (grey)
Partially Malleabilized Iron
 Incomplete Ferritizing Anneal
Ferritic Matrix
Ferrite (White)
Graphite (black)
10 m
Fully Malleabilized Iron
 Complete Ferritizing Anneal
6) Good wear resistance and vibration damping capacity.
7) Can be used from – 60 to 1200°F
8) Solidification range of 2550-2065°F
9) Low moderate cost.
10)M.C.I. contains 2-3% C, 0.6 -1.3% Si, 0.2 -0.6% Mn, 0.15% P and
0.10% S.
Application
1)
Automotive Industry
2)
Rail Road
3)
Agricultural implements
4)
Electrical line Hardware
5)
Conveyor chain links
6)
Gear case
7)
Universal joint yoke
8)
Rear axle banjo housing
9)
Automotive crankshaft.
Spheroidal Cast Iron
Nodular (ductile) iron: the dark graphite nodules are
surrounded by an -ferrite matrix.
Spheroidal Cast Iron
• Nodular or ductile cast iron. Tiny amounts of magnesium or cerium
added to these alloys slow down the growth of graphite precipitates by
bonding to the edges of the graphite planes.
• Along with careful control of other elements and timing, this allows the
carbon to separate as spheroidal particles as the material solidifies.
• The properties are similar to malleable iron, but parts can be cast with
larger sections.
Characteristics:
1)
Unlike long flakes as in G.S.I., graphite appears as rounded particles,
or nodules or spheroids in N.C.I.
2)
Ductile cast iron possesses very good machinablity.
3)
Soft annealed grades of S.C.I. can be turned at very high feeds and
speeds.
4)
The properties of S.C.I. depend upon the metal composition and the
cooling rate.
5)
Spheroidal or Nodular or Ductile C.I. contains 3.2%-4.2% C, 1.1%-3.5%
Si, 0.3% - 0.8% Mn, 0.08% P and 0.2% S.
6)
It possesses excellent damping capacity, casteblity and wear
resistance.
Mechanical Properties of SG Iron
Application
1)
Paper industries machinery
2)
I. C. engines
3)
Power transmissions equipment
4)
Farm implements and tractors
5)
Earth moving machinery
6)
Valves and fittings
7)
Steel mills rolls and mill equipment
8)
Pipes
9)
Pumps and compressors
White Cast iron
White iron: the light cementite regions are surrounded by
pearlite, which has the ferrite–cementite layered structure.
White cast iron
• With a lower silicon content and faster cooling, the carbon in white
cast iron precipitates out of the melt as the metastable phase
cementite, Fe3C, rather than graphite.
• The cementite which precipitates from the melt forms as relatively
large particles, usually in a eutectic mixture, where the other phase
is austenite (which on cooling might transform to martensite).
• It is difficult to cool thick castings fast enough to solidify the melt as
white cast iron all the way through.
• However, rapid cooling can be used to solidify a shell of white cast
iron, after which the remainder cools more slowly to form a core of
grey cast iron.
Characteristics:
1)
W.C.I. derives its name from the fact that its freshly broken surface
shows a bright white fracture.
2)
Unlike gray iron, W.C.I. has almost all its carbon chemically bonded
with the iron- as iron carbide, Fe3C which is very hard and brittle
constituent.
3)
W.C.I. possesses excellent abrasive wear resistance.
4)
W.C.I. under normal circumstances is brittle and not machinable.
5)
By using a fairly low silicon content, cast iron may be made to solidify
as white iron.
6)
W.C.I. casting can be made in sand moulds.
7)
W.C.I. can also be made on the surface of a gray iron casting provided
the material is of special composition.
8)
If iron of proper composition is cooled rapidly, the free carbon will
go in the combined form and give rise to white iron casting.
9)
W.C.I. contains 1.8-3.6% C, 0.5 – 2.0% Si, 0.2- 0.8% Mn, 0.18% P
and 0.10% S.
10) The solidification range of W.C.I. is 2550-2065°F
Application
1)
For producing malleable iron casting
2)
For manufacturing those component parts which require a hard
and abrasion resistant material.
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